This invention relates to heat recovery devices, and, more particularly, to the plate packs and baskets used in regenerative heat recovery devices.
In a conventional fossil-fuel power plant, coal, oil, or gas is burned in a boiler. The resulting exhaust gas heats water to steam, and the steam turns a turbine/generator to produce electric power. The exhaust gas is directed through a heat recovery device, sometimes termed an air preheater, which transfers heat from the exhaust gas to an incoming flow of air. The preheated air flow is introduced into the boiler as the source of oxygen for combustion. Preheating of the incoming air flow improves thermal efficiency of the boiler and also reduces thermal effluent of the power plant.
The most common type of heat recovery device used for air preheating in power plants is a rotary regenerative heat exchanger. In such a heat exchanger, a large wheel is driven to rotate on a shaft. The wheel is filled with heat exchange elements that travel in circular paths with the wheel. A conduit system directs hot exhaust gas to the heat exchange elements during a first portion of their cycle of rotation, and directs cool incoming air to the heat exchange elements during a second portion of their cycle of rotation. Heat is transferred from the hot exhaust gas to the heat exchange elements during the first portion of the cycle of rotation, and heat is transferred from the heat exchange elements to the incoming air during the second portion of the cycle of rotation. Since the process is continuous, the incoming air is continuously heated as it flows around the heat exchange elements.
In a favored design, the heat exchange elements are thin steel plates having a symmetrically ridged configuration. The plates are supported in baskets rather than with fixed fasteners. This approach minimizes damage from thermal stresses and strains and permits the cleaning and replacement of the heat exchange elements as necessary.
The plate packs of the heat exchanger elements are engineered to maximize heat transfer and minimize pressure drop, and also to minimize the effects of fouling of the heat exchanger plates due to deposition of particulate (also called "fly ash") from the exhaust gas onto the plates. When the exhaust gas passes through the heat exchanger, it often has not yet been subjected to electrostatic precipitation or other treatment to remove excessive amounts of particulates produced during combustion. Deposition of the particulate onto the plates, which reduces their gas flow and heat transfer efficiency, is therefore a consideration in design of the plate packs. It is also desirable to permit periodic cleaning of the plates by soot blowing techniques to remove accumulated particulate.
While a number of designs for heat exchanger plates have been advanced, these designs suffer from shortcomings in their combination of fouling, pressure drop, heat transfer, and cleaning characteristics. There is therefore an ongoing need for improved plate and plate pack designs. The present invention fulfills this need, and further provides related advantages.